Imaging optical system and projection exposure system for microlithography

ABSTRACT

An imaging optical system includes a plurality of mirrors that image an object field in an object plane into an image field in an image plane. At least one of the mirrors is obscured, and thus has an opening for imaging light to pass through. The fourth-last mirror in the light path before the image field is not obscured and provides, with an outer edge of the optically effective reflection surface thereof, a central shadowing in a pupil plane of the imaging optical system. The distance between the fourth-last mirror and the last mirror along the optical axis is at least 10% of the distance between the object field and the image field. An intermediate image, which is closest to the image plane, is arranged between the last mirror and the image plane. The imaging optical system can have a numerical aperture of 0.9. These measures, not all of which must be effected simultaneously, lead to an imaging optical system with improved imaging properties and/or reduced production costs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT/EP2008/008381, filed on Oct.2, 2008, which claims benefit of Provisional Application No. 60/982,785,filed on Oct. 26, 2007, and to German Application No. 10 2007 051 670.5,filed Oct. 26, 2007. The entire contents of each of the above-referencedapplications is incorporated herein by reference.

The disclosure relates to imaging optical systems, to projectionexposure systems including an imaging optical system, methods forproducing microstructured components, and microstructured componentsproduced with these methods.

BACKGROUND

Examples of imaging optical systems are described in U.S. Pat. No.6,750,948 B2, US 2006/0232867 A1, EP 0 267 766 A2, U.S. Pat. No.7,209,286 B2 and WO 2006/069 725 A1.

In particular for use within a projection exposure system formicrolithography, in particular for the production of microstructured ornano-structured semiconductor components, there is a need for improvedimaging properties of imaging optical systems. For example, in imagingoptical systems composed of mirrors, it can be desirable to provide agreater numerical aperture or a better correction of imaging errors.Alternatively or additionally, there is a need for simpler manufactureof mirrors at pre-specified dimensions, or for a mirror arrangement thatrelaxes the requirements on the production of the mirror support inparticular, at least for individual mirrors. For example, the number ofoptical elements required for the imaging and for the correction ofimaging errors should be kept as low as possible.

SUMMARY

It has been found that imaging optical systems having a mirror thatdetermines, with the outer edge thereof and not with an opening, a pupilobscuration of an obscured optical system, can provide high-apertureobjectives with well-corrected imaging errors. The outer edge of themirror (e.g., which can be a fourth-last mirror in the light path of theimaging optical system) which surrounds the optically effectivereflection surface thereof, is either the outer edge of the opticallyeffective reflection surface itself, or the outer edge of a substrate onwhich the reflection surface is provided, or the outer edge of amechanical holding structure supporting the reflection surface or thesubstrate.

A convex fourth-last mirror in the light path of the imaging opticalsystem can allow the imaging optical system to be constructed withrelatively low pupil obscuration.

In some embodiments, it is possible to apply an aperture stop to thefourth-last mirror in the light path.

In some embodiments, an advantageously large space is present betweenthe fourth-last and last mirrors. Such embodiments can advantageouslyavoid problems associated with other imaging optical systems havingobscured mirrors and a high numerical aperture in which the regionbetween the fourth-last and the last mirror was a problematically smallmeaning that either only very thin mirrors or a mirror which was veryexpensive to produce, comprising reflective coatings on both sides,could be used there.

In certain embodiments, moving the intermediate image plane in thedirection of an image plane of the imaging optical system leads, bycomparison with other constructions, to reduced requirements on theoptical effect of the last two mirrors of the imaging optical system. Incontrast, in certain known obscured systems, the intermediate imageplane is often spatially arranged at approximately the height of thelast mirror in the light path. It has been found that this is not acompulsory requirement because the last mirror in the light path ismostly not decisive as regards the pupil obscuration, in such a way thata relatively large central opening, and thus an intermediate planeseparated from the reflection surface of the penultimate mirror, can betolerated there.

In some embodiments, a distance between an intermediate image and theimage plane, along the optical axis, is at most 0.95 times the distance,from the image plane, of the last mirror in the light path. A distancefrom the image plane of the last mirror in the light path is defined asthe distance from the image plane of the piercing point of an opticalaxis of the imaging optical system through the reflection surface ofthis mirror. In the case where the optical axis does not pass throughthe reflection surface of the mirror, i.e., in the case, for example, ofan off-axis mirror, the piercing point of the optical axis through asurface which carries on continuously in accordance with the opticaldesign input is selected instead of the piercing point of the opticalaxis through the reflection surface. If the mirror is rotationallysymmetric about the optical axis, this piercing point coincides with thecentre of the reflection surface of the mirror. In the case where thislast mirror is obscured, the centre of the reflection surface may alsolie in the obscuration opening, in which case it is assumed that thereflection surface carries on continuously within the obscurationopening in accordance with the optical design input. The distance of theintermediate image plane from the image plane may for example, be 0.7,0.8 or 0.9 times the distance of the last mirror in the light path fromthe image plane.

In some embodiments, imaging optical systems have a numerical apertureof at least 0.4 (e.g., at least 0.5, at least 0.6, at least 0.9).

In certain embodiments, imaging optical systems include fewer than 10mirrors and have a numerical aperture of ≧0.7.

In some embodiments, imaging optical systems include exactly eightmirrors and have a numerical aperture of 0.9.

Imaging optical systems can have a maximum root mean square (rms)wavefront error of less than 10 nm (e.g., less than 5 nm, less than 2nm, less than 1 nm, less than 0.5 nm).

Such imaging properties can be advantageous for achieving a high localresolution over the whole field. These imaging properties can beindependent of the wavelength of the imaging light. The wavelength ofthe imaging light can range from the EUV range to the visible spectrum.Wavefront errors are preferred which lead to a diffraction limitedresolution and which are therefore, in particular, less than onefourteenth of the imaging light wavelength. For EUV wavelengths, awavefront error which has a root mean square (rms) of less than 1 nmleads to a resolution which is, in practice, diffraction limited.

In some embodiments, the imaging optical system has a maximum distortionof less than 10 nm (e.g., less than 2 nm, less than 0.5 nm).

In certain embodiments, the imaging optical system has a pupilobscuration of less than 20% (e.g., less thank 15%, less than 10%).

A low pupil obscuration, i.e., the proportion of the pupil surface whichcannot be used because of the central pupil obscuration, can lead to anadvantageously high light throughput for the imaging optical system.Additionally, an imaging optical system with a low pupil obscuration canbe more widely used, because the lower the pupil obscuration, thegreater the bandwidth of the available illumination mechanism. Imagingoptical systems with low pupil obscurations therefore providehigh-contrast imaging substantially independently of the type of objectstructure to be imaged.

Field planes arranged parallel to one another can facilitate theintegration of the imaging optical system into structural surroundings.This advantage may be particularly significant when the imaging opticalsystem is used in a scanning projection exposure system, since the scandirections can then be guided parallel to one another.

In certain embodiments, imaging optical systems can have an image fieldlarger than 1 mm² (e.g., having side lengths of 1 mm and 13 mm). Suchimage field sizes can lead to a good throughput when the imaging opticalsystem is used in a projection exposure system. Other dimensions of thelong and short image field sides are also possible. The short imagefield sides may also be less than 1 mm or greater than 1 mm. The longimage field sides may, for example, also be 5 mm, 10 mm or 15 mm.

Imaging optical systems can have a reduction image scale of eight. Suchan imaging scale can allow a low angle of incidence on a reflection maskwhen using the imaging optical system in a projection exposure system.In this type of application, the use of an imaging scale of this typedoes not lead to the requirement of unnecessarily large masks.

In some embodiments, an odd number of obscured mirrors are used. Forexample, three mirrors could be obscured.

Imaging optical systems can include at least one intermediate image,e.g., positioned at a plane folded in the vicinity of a pupil plane(e.g., coinciding with the pupil plane). Such an arrangement can lead tothe possibility, in a spatially restricted arrangement, of exertinginfluences both in a field plane and in a pupil plane of the imagingoptical system. This can be particularly expedient for correctionpurposes.

Principal rays of imaging optical systems can extend divergently toneighbouring field points in the light path from an object plane of theimaging optical system to he first mirror in the light path. Suchembodiments can lead to the possibility of supplying on the imagingoptical system, directly and without the interposition of additionalimaging elements, from a preceding illumination optical system via apupil component which is the last element before the imaging opticalsystem, it then being possible for this pupil component to be arrangedin the pupil plane of the imaging optical system, which plane isdisposed so as to precede the imaging optical system.

In certain embodiments, imaging optical systems include exactly sixmirrors and form two intermediate images. Such embodiments can be usedon the one hand for compact beam guidance and also, on the other hand,for correction purposes.

Projection exposure systems can include an imaging optical system, alight source, and an illumination optical system for guiding light fromthe light source to the imaging optical system. The light source of theprojection exposure system may be in the form of a broadband lightsource and may have, for example, a bandwidth greater than 1 nm, greaterthan 10 nm or greater than 100 nm. In addition, the projection exposuresystem may be constructed in such a way that it can be operated withlight sources of different wavelengths. Light sources for otherwavelengths, in particular wavelengths used for microlithography, can beused in conjunction with the imaging optical system, for example lightsources with wavelengths of 365 nm, 248 nm, 193 nm, 157 nm, 126 nm and109 nm, and in particular also with wavelengths which are less than 100nm.

In certain aspects, the invention features methods for producing amicrostructured component that include providing a reticle and a wafer,projecting a structure on the reticle onto a light sensitive layer ofthe a wafer by using a projection exposure system, and producing amicrostructure on the wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be described in the following in greater detail withreference to the drawings, in which:

FIG. 1 is a schematic view of a projection exposure system for EUVmicrolithography;

FIG. 2 is a view of an embodiment of an imaging optical system, inmeridional section.

FIG. 3 is a view of an embodiment of an imaging optical system, inmeridional section.

FIG. 4 is a view of an embodiment of an imaging optical system, inmeridional section.

FIG. 5 is a view of an embodiment of an imaging optical system, inmeridional section.

FIG. 6 is a view of an embodiment of an imaging optical system, inmeridional section.

FIG. 7 is a view of an embodiment of an imaging optical system, inmeridional section.

DETAILED DESCRIPTION

A projection exposure system 1 for microlithography has a light source 2for illumination light. The light source 2 is an EUV light source whichproduces light in a wavelength range in particular of between 10 nm and30 nm. Other EUV wavelengths are also possible. In general, any desiredwavelengths, for example visible wavelengths or any other wavelengthswhich are used, for example, in microlithography and are available forthe appropriate laser light sources and/or LED light sources (forexample 365 nm, 248 nm, 193 nm, 157 nm, 129 nm or 109 nm), are possiblefor the illumination light guided in the projection exposure system 1. Alight path of the illumination light 3 is shown extremely schematicallyin FIG. 1.

An illumination optical system 6 guides the illumination light 3 fromthe light source 2 to an object field 4 (cf. FIG. 2) in an object plane5. The object field 4 is imaged into an image field 8 (cf. FIG. 2) in animage plane 9, at a pre-specified reduction scale, with a projectionoptical system 7. Embodiments shown in FIGS. 2 to 7 may be used for theprojection optical system 7. The projection optical system 7 shown inFIG. 2 has a reduction factor of 8. Other reduction scales are alsopossible, for example 4×, 5×, or even reduction scales that are greaterthan 8×. An imaging scale of 8× is particularly suitable forillumination light 3 with an EUV wavelength, since the object-side angleof incidence on a reflection mask 10 can thus remain small. An imagingscale of 8× also may not need the use of unnecessarily large masks. Inthe projection optical system 7 in the embodiments shown in FIGS. 2 to7, the image plane 9 is arranged parallel to the object plane 5. Aportion of the reflective mask 10, also known as a reticle, coincidingwith the object field 4 is hereby imaged.

The image field 8 is bent in an arc shape, the distance between the twoarcs which delimit the image field 8 being 1 mm. 1 mm is also the sidelength of the straight side edges which delimit the image field 8between the two arcs and which extend parallel to one another. These twostraight side edges of the image field 8 are at a distance of 13 mm fromone another. The surface of this curved image field corresponds to arectangular image field with side lengths of 1 mm×13 mm. A square imagefield 8 of this type is also possible.

Imaging takes place on the surface of a substrate 11 in the form of awafer which is supported by a substrate holder 12. In FIG. 1, a lightbeam 13 of the illumination light 3 entering the projection opticalsystem 7 is shown schematically between the reticle 10 and theprojection optical system, and a light beam 14 of the illumination light3 exiting from the projection optical system 7 is shown schematicallybetween the projection optical system 7 and the substrate 11.

The image field-side numerical aperture of the projection optical system7 shown in FIG. 2 is 0.9. This is not reproduced to scale in FIG. 1 forvisual reasons.

In order to aid the description of the projection exposure system 1 andthe various embodiments of the projection optical system 7, an xyzCartesian coordinate system is provided in the drawings and shows therespective locations of the components represented in the figures. InFIG. 1, the x direction extends perpendicular to and into the drawingplane. The y direction extends to the right and the z direction extendsdownwards.

The projection exposure system 1 is a scanner-type device. Both thereticle 10 and the substrate 11 are scanned in the y direction duringoperation of the projection exposure system 1.

FIG. 2 shows the optical construction of a first embodiment of theprojection optical system 7. The light path of each of two individualrays 15, which proceed in each case from two object field points in FIG.2 and are distanced from one another in the y direction, is shown. Thetwo individual rays 15, which belong to one of these two object fieldpoints, are each associated with two different illumination directionsfor the two image field points. The individual rays 15, associated withthe same illumination direction, of different field points extenddivergently proceeding from the object plane 5. This is also referred toin the following as a negative input back focal length or a negativeback focal length of the entrance pupil. An entrance pupil of theprojection optical system 7 shown in FIG. 2 lies not inside theprojection optical system 7, but before the object plane 5 in the lightpath. This makes it possible, for example, to arrange a pupil componentof the illumination optical system 6 in the entrance pupil of theprojection optical system 7, before the projection optical system 7 inthe light path, without further imaging optical components having to bepresent between these pupil components and the object plane 5.

The projection optical system 7 shown in FIG. 2 has a total of eightmirrors, which are numbered in the sequence of the light path,proceeding from the object field 4, as M1 to M8. FIG. 2 shows only thecalculated reflection surfaces of the mirrors M1 to M8.

The optical data for the projection optical system 7 shown in FIG. 2 areshown in the following via two tables. In the column “radius”, the firsttable shows in each case the radius of curvature of the mirrors M1 toM8. The third column (thickness) describes the distance, proceeding fromthe object plane 5, to the following surface in each case.

The second table describes the precise surface form of the reflectionsurfaces of the mirrors M1 to M8, where the constants K and A to J areto be put into the following equation for the sagittal height:

${z(h)}=={\frac{{ch}^{2}}{1 + {{SQRT}\left\{ {1 - {\left( {1 + K} \right)c^{2}h^{2}}} \right\}}} + {Ah}^{4} + {Bh}^{6} + {Ch}^{8} + {Dh}^{10} + {Eh}^{12} + {Fh}^{14} + {Gh}^{16} + {Hh}^{18} + {Jh}^{20}}$

In this case, h represents the distance from the optical axis 19.Therefore: h²=x²+y². The reciprocal of “radius” is used for c.

Surface Radius (1/c) Thickness Operating mode Object plane infinity517.466 M1 −460.153 −217.028 REFL M2 −380.618 101.780 REFL M3 304.428−158.351 REFL M4 248.577 786.055 REFL M5 320.928 −512.457 REFL M6826.181 1504.412 REFL M7 −3221.704 −191.095 REFL stop infinity −375.302M8 750.83 606.397 REFL Image plane infinity 0

Surface K A B C D M1  0.000000E+00 −1.631597E−10  9.657530E−16−6.306626E−20  1.072197E−24 M 2 −7.342117E+00 −3.247790E−08 1.007295E−13 −2.908653E−18 −6.581368E−21 M 3 −8.421287E+00 1.604616E−09  1.164266E−11 −7.638324E−15  2.158838E−18 M 4 5.504873E−02 −2.854695E−10  1.302845E−15  7.411326E−19 −1.319473E−22 M5 −2.441303E−02 −4.072151E−09 −5.877441E−14  2.214912E−18 −8.175465E−23M 6  3.411049E−03 −7.680740E−12 −7.621133E−18 −6.837917E−24−8.305886E−30 M 7 −2.544754E+00  5.119174E−10 −8.412525E−16 8.746864E−21 −4.053738E−26 M 8  1.012485E−01 −6.355004E−11−1.261118E−16 −6.586951E−24 −4.143278E−28 Surface E F G H J M1−1.289213E−29  8.646860E−35 −2.746050E−40 0.000000E+00  1.075412E−51 M21.743214E−24 −2.256980E−28   1.288821E−32 0.000000E+00 −2.146208E−41 M32.665732E−25 1.001342E−24 −1.896580E−27 1.213404E−30 −2.772775E−34 M41.642304E−26 −1.185339E−30   4.697782E−35 −7.812489E−40   0.000000E+00M5 1.783031E−27 −3.302179E−32   6.356237E−37 −8.439168E−42  3.970026E−47 M6 −1.193959E−35  3.014822E−41 −1.666695E−46 2.921935E−52−2.589560E−58 M7 1.405577E−31 1.660762E−37 −4.750000E−42 2.390150E−47−4.132019E−53 M8 3.396965E−35 3.588060E−40 −3.053788E−45 6.807302E−51−1.109855E−56

The mirrors M1, M2 and M4 of a first mirror group 18, which includes themirrors M1 to M4, are shaped as ring segments and are used off-axis withrespect to the optical axis 19—completely in the case of the mirrors M1and M2 and for the most part in the case of the mirror M4. The employedoptical reflection surface of the mirrors M, M2 and—for the most part—M4thus lies at a distance from the optical axis 19. The reflectionsurfaces of all the mirrors M1 to M8 are rotationally symmetric aboutthe optical axis 19.

The employed reflection surface of the mirror M3 is approximatelycentred on the optical axis 19 (on-axis).

The mirrors M1, M4, M6, M7 and M8 are concave mirrors. The mirrors M2,M3 and M5 are convex mirrors.

An intermediate image plane 20 of the projection optical system 7 liesbetween the mirrors M4 and M5. As their course continues, the individualrays 15 pass through an opening 21 in the mirror M6. The mirror M6 isused around opening 21. The mirror M6 is thus an obscured mirror. Aswell as the mirror M6, the mirrors M7 and M8 are also obscured and bothlikewise include a opening 21.

The mirror M5, i.e. the fourth-last mirror in the light path before theimage field 8, is not obscured and thus has no opening for imaginglight. An outer edge 22 of the optically effective reflection surface ofthe mirror M5 provides a central shadowing of the projection opticalsystem 7, i.e., of the imaging optical system, in the pupil plane 17.The mirror M5 therefore shadows the light path between the mirrors M6and M7.

The mirror M5 is arranged on the optical axis 19 and lies approximatelycentrally on the optical axis 19.

In the embodiment shown in FIG. 2, the distance between the mirror M5and the last mirror M8, which are arranged back-to-back in terms of thereflective effect thereof, is approximately 20.6% of the distancebetween the object plane 5 and the image plane 9 and, in particular,approximately 20% of the marginally greater distance between the objectfield 4 and the image field 8. A substantially greater space is thuspresent in the optical system 7 between the mirrors M5 and M8.

A further intermediate plane 23 lies between the mirror M6 and themirror M7 in the light path. This is the intermediate image plane whichis closest to the image plane 9. This intermediate image plane 23 liesspatially between the last mirror M8 in the light path and the imageplane 9. The distance of the intermediate image plane 23 from the imageplane 9 is approximately 0.7 times the distance of the last mirror M8 inthe light path from the image plane 9.

The projection optical system 7 shown in FIG. 2 has a maximum root meansquare (rms) wavefront error of 0.9 nm. The distortion of the projectionoptical system 7 is at most 0.5 nm. The pupil obscuration, i.e., theratio of a central shadowed surface portion in the pupil plane 17 to thewhole surface within an illuminated edge contour in the pupil plane 17,is 11.6%.

FIG. 3 shows a further embodiment of a projection optical system 7.Components and features which correspond to those that have previouslybeen described with reference to FIGS. 1 and 2 have the same referencenumerals and will not be discussed in detail again.

The optical data for the projection optical system 7 shown in FIG. 3 areshown in the following via two tables, which correspond in layout to thetables for FIG. 2.

Surface Radius (1/c) Thickness Operating mode Object plane infinity240.357 M1 306.212 −140.357 REFL M2 472.863 1508.127 REFL M3 −1214.568−651.640 REFL M4 371.570 1076.156 REFL M5 210.825 −524.516 REFL M6793.298 1450.998 REFL M −3402.480 −176.337 REFL stop infinity −366.873M8 734.006 584.084 REFL Image plane infinity 0.000

Surface K A B C D M1 0.000000E+00  5.528998E−09 −4.968534E−131.659177E−17 −3.863442E−22 M2 −6.538633E−01   5.913642E−10 −2.068085E−151.843758E−20 −6.714355E−26 M3 0.000000E+00  9.809893E−10  1.757665E−156.252623E−20 −7.383824E−25 M4 2.740280E+00 −4.880461E−08  8.522603E−12−1.221389E−15   1.142980E−19 M5 −5.973645E−02  −1.313275E−08−1.603339E−13 2.016611E−18 −4.373542E−22 M6 4.517989E−02 −1.639817E−11−1.843198E−17 −2.050197E−23  −3.219956E−29 M7 −1.286534E+01  4.603123E−10 −1.024577E−15 1.178213E−20 −7.426445E−26 M8 9.856773E−02−8.505963E−11 −1.255661E−16 −1.224739E−22  −3.390517E−28 Surface E F G HJ M1 5.540209E−27 −4.791768E−32 2.229758E−37 −4.553644E−43 0.000000E+00M2 1.572034E−31 −1.728552E−37 1.501360E−43  0.000000E+00 0.000000E+00 M38.354870E−30 −3.768113E−35 0.000000E+00  4.020897E−45 0.000000E+00 M4−6.828562E−24   2.234887E−28 −2.050695E−33  −5.185597E−38 0.000000E+00M5 2.682717E−26 −1.836495E−30 8.559900E−35 −1.643140E−39 0.000000E+00 M62.845752E−35 −2.880170E−40 5.575425E−46 −7.139928E−52 0.000000E+00 M74.719915E−31 −2.246586E−36 6.923567E−42 −9.256971E−48 0.000000E+00 M85.071111E−34 −2.813625E−39 6.372889E−45 −9.981207E−51 0.000000E+00

The embodiment shown in FIG. 3 differs from that shown in FIG. 2 byvirtue of the arrangement of the first mirror group 18 including themirrors M1 to M4. All four mirrors M1 to M4 of the first mirror group 18of the projection optical system 7 shown in FIG. 3 are supplied off-axisvia a light source. The mirror M1 is convex and the mirrors M2 to M4 areconcave.

The projection optical system 7 shown in FIG. 3 has a negative backfocal length of the entrance pupil. In other words, object plane 5 ispositioned along optical axis 19 between the entrance pupil and themirrors composing projection optical system 7.

The first intermediate image plane 20 is arranged in the region of themirror M4 in the embodiment shown in FIG. 3. According to the preciseconfiguration of the mirror construction, the associated intermediateimage can be arranged before the mirror M4, on the mirror M4, or evenafter the mirror M4.

In the embodiment shown in FIG. 3, the mirror M3 lies not to the left ofthe mirror M6, as in the embodiment shown in FIG. 2, but at the level ofthe optical axis 19 to the right of the mirror M6. The rays 15 passthrough the mirror M6 on the way from the mirror M2 to the mirror M3,exactly like the rays 15 on the way from the mirror M3 to the mirror M4and on the way from the mirror M4 to the mirror M5. The opening 21 inthe mirror M6 is thus passed through thrice by the individual rays 15.

In the projection optical system 7 shown in FIG. 3, the distance betweenthe mirrors M5 and M8 is approximately 12.8% of the distance between theobject plane 5 and the image plane 9. The distance of the intermediateimage plane 23 from the image plane 9 is approximately 0.8 times thedistance of the last mirror M8 in the light path from the image plane 9.

The maximum (rms) wavefront error of the projection optical system 7shown in FIG. 3 is 2.2 nm. The maximum distortion is 5 nm. The pupilobscuration is 8.4%.

FIG. 4 shows a further embodiment of a projection optical system 7.Components and features which correspond to those that have previouslybeen described with reference to FIGS. 1 and 2 have the same referencenumerals and will not be discussed in detail again.

The optical data for the projection optical system 7 shown in FIG. 4 areshown in the following via two tables, which correspond in layout to thetables for FIG. 2.

Surface Radius (1/c) Thickness Operating mode Object plane infinity390.160 M1 5657.607 −290.160 REFL M2 547.829 364.027 REFL M3 150.329−131.050 REFL M4 182.077 674.854 REFL M5 301.845 −517.671 REFL M6809.621 1464.069 REFL M7 −3032.589 −177.803 REFL stop infinity −377.065M8 753.606 600.638 REFL Image plane infinity 0.000

Surface K A B C D M1 0.000000E+00 −2.662522E−10 −5.535133E−15 9.951400E−20 −1.728701E−24 M2 0.000000E+00 −7.758511E−11 −4.927920E−16−2.380995E−21  1.771881E−27 M3 0.000000E+00  2.187978E−08 −4.324024E−12−2.166837E−15  6.601874E−19 M4 0.000000E+00  1.844448E−09  6.801387E−14 2.528119E−17 −6.128096E−21 M5 1.156883E−04 −6.361997E−09 −4.599504E−14 1.885582E−18 −6.053781E−23 M6 3.259720E−02 −1.077005E−11 −1.049275E−17−1.178590E−23 −1.688268E−30 M7 −8.103305E+00   3.958094E−10−5.118462E−16  5.066772E−21 −1.825272E−26 M8 1.035316E−01 −7.996215E−11−1.253165E−16 −7.448536E−23 −2.060928E−28 Surface E F G H J M1 1.574353E−29 −5.663846E−35 0.000000E+00 0.000000E+00 0.000000E+00 M2−1.673915E−31  0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 M3−1.166941E−23 −9.288602E−26 5.378119E−29 0.000000E+00 0.000000E+00 M4 1.073882E−24 −9.788111E−29 3.783735E−33 0.000000E+00 0.000000E+00 M5−4.369093E−28  5.123232E−32 −7.255963E−37  0.000000E+00 0.000000E+00 M6−6.033318E−35  1.025297E−40 −1.418317E−46  0.000000E+00 0.000000E+00 M7 1.004654E−31 −5.423670E−37 2.038001E−42 −3.000000E−48  0.000000E+00 M8−4.980960E−34  5.995233E−40 6.787033E−46 −4.632967E−51  0.000000E+00

The projection optical system 7 shown in FIG. 4 also differs from thoseshown in FIG. 2 and FIG. 3 substantially by virtue of the arrangement ofthe first mirror group 18 comprising the mirrors M1 to M4. The mirrorsM1, M2 and M4 are supplied off-axis. The mirror M3 is convex. Themirrors M1, M2 and M4 are convex. The mirror M1 has such a low curvaturethat the mirror may not only be concave, but with a slight adaptation ofthe construction may also be planar or convex.

In the projection optical system 7 of FIG. 4, the first intermediateimage plane 20 lies in the light path between the mirrors and M4 and M5,approximately at the level of the mirror M3.

In the embodiment shown in FIG. 4, the mirror M3 is again arranged tothe left of the mirror M6, in such a way that the opening 21 of themirror M6 is only passed through once by the rays 15. With a slightadaptation of the construction, the mirror M3 may also be moved into theopening of the mirror M6.

In the projection optical system 7 shown in FIG. 4, the distance betweenthe mirrors M5 and M8 is approximately 19.6% of the distance between theobject plane 5 and the image plane 9. The distance of the intermediateimage plane 23 from the image plane 9 is approximately 0.76 times thedistance of the last mirror M8 in the light path from the image plane 9.

The maximum (rms) wavefront error of the projection optical system 7shown in FIG. 4 is 1.4 nm. The maximum distortion is 1.5 nm. The pupilobscuration is 10.9%.

FIG. 5 shows a further embodiment of a projection optical system 7.Components and features which correspond to those which have previouslybeen described with reference to FIGS. 1 and 2 have the same referencenumerals and will not be discussed in detail again.

The optical data for the projection optical system 7 shown in FIG. 5 areshown in the following via two tables, which correspond in layout to thetables for FIG. 2.

Surface Radius (1/c) Thickness Operating mode Object plane infinity591.532 M1 −6782.876 −530.662 REFL M2 702.707 1026.755 REFL stopinfinity 0.000 M3 217.303 −507.993 REFL M4 776.996 1490.702 REFL M5−2014.188 −533.319 REFL M6 791.740 603.252 REFL Image plane infinity0.000

Surface K A B C M1  0.000000E+00 8.899437E−09 −1.356259E−12 2.954130E−15M2 −3.639089E+00 1.110645E−09 −2.542191E−15 2.297600E−20 M3 1.390154E−01 −1.972567E−08   3.444974E−13 −7.400803E−17  M4−2.088645E−02 −1.996767E−11  −3.060841E−17 −4.632700E−23  M5−1.390893E+01 1.114680E−09  1.108176E−15 5.215888E−20 M6  1.112425E−016.540015E−11  8.340321E−17 2.310935E−22 Surface D E F G M1 −2.165883E−180.000000E+00  6.325365E−25 −1.919429E−28 M2 −1.439457E−24 9.400607E−29−3.212860E−33  4.384528E−38 M3  9.862318E−21 −2.518066E−24  3.734400E−28 −2.241749E−32 M4 −5.236534E−29 −6.140963E−35 −6.134373E−40  8.521628E−46 M5 −1.658708E−24 7.482784E−29 −1.911769E−33 1.936176E−38 M6 −2.192695E−27 6.492849E−33  1.784557E−37 −1.082995E−42

The projection optical system 7 shown in FIG. 5 has a total of sixmirrors, which are numbered in the sequence of the light path,proceeding from the object field 5, as M1 to M6.

In the projection optical system 7 shown in FIG. 5, a first mirror group24 includes only two mirrors, namely the mirrors M1 and M2. The mirrorM1 is supplied approximately on-axis and the mirror M2 is suppliedoff-axis. The following mirrors M3 to M6 correspond in arrangement andfunction to the mirrors M5 to M8 of the embodiments shown in FIGS. 2 to4.

The projection optical system 7 shown in FIG. 5 has a numerical apertureof 0.4.

The projection optical system 7 according to FIG. 5 has a positive backfocal length for the entrance pupil, i.e., principal rays 16 extendinginitially convergently from the object field 4. The mirror M1 lies inthe region of an entrance pupil plane 25 of the projection opticalsystem 7. The first intermediate image plane 20 also lies between themirrors M2 and M3, likewise approximately at the level of the mirror M1.

The mirror M1 is arranged in the opening 21 of the mirror M4. Theopening 21 of the mirror M4 is again passed through thrice, similarly tothe mirror M6 in the embodiment shown in FIG. 3.

The fourth-last mirror M3, the outer edge 22 of which again provides thepupil obscuration of the projection optical system 7 shown in FIG. 5,lies in the region of a further pupil plane 26 of the projection opticalsystem 7 shown in FIG. 5. An aperture stop of the projection opticalsystem 7 according to FIG. 5 can therefore be applied to the mirror M3.

The distance between the fourth-last mirror M3 and the last mirror M6 isequal to approximately 21.0% of the distance between the object plane 5and the image plane 9 in the embodiment shown in FIG. 5. The distance ofthe intermediate image plane 23 from the image plane 9 is approximately0.74 times the distance of the last mirror M6 in the light path from theimage plane 9.

The projection optical system 7 shown in FIG. 5 has a maximum (rms)wavefront error of 0.4 nm. The maximum distortion is 0.3 nm. The pupilobscuration is 17.6%.

FIG. 6 shows a further embodiment of a projection optical system 7.Components and features which correspond to those which have previouslybeen described with reference to FIGS. 1 to 5 have the same referencenumerals and will not be discussed in detail again.

The optical data for the projection optical system 7 shown in FIG. 6 areshown in the following via two tables, which correspond in layout to thetables for FIG. 2.

Surface Radius (1/c) Thickness Operating mode Object plane infinity683.665 M1 −694.834 −271.324 REFL M2 −411.527 1372.036 REFL M3 346.281−1100.613 REFL M4 1469.502 2005.780 REFL M5 −722.731 −41.563 REFL stopinfinity −272.149 M6 544.465 370.467 REFL Image plane infinity 0.000

Surface K A B C M1  7.396949E−03 −8.591818E−11  2.958631E−15−1.515085E−19 M2 −4.696303E−01 −1.639186E−09 −1.894486E−14 −4.136066E−18M3 −5.224549E−01 −2.010111E−09 −1.293006E−14 −2.918315E−20 M4−3.021297E−02  9.250522E−14  5.057734E−20  4.887335E−28 M5 −3.126684E+00 2.153833E−09  1.799694E−14 −1.892202E−20 M6  6.984230E−01 −1.682769E−10−1.422157E−15  1.234832E−20 Surface D E F G M1 4.091038E−24−5.790509E−29 3.296826E−34  8.178384E−41 M2 1.255234E−21 −1.379809E−255.435466E−30 −4.566966E−36 M3 1.475407E−23 −5.835055E−28 1.288505E−32−3.671165E−37 M4 4.320243E−35  4.670696E−39 −4.109431E−45   2.963010E−51M5 −6.296522E−25   2.964336E−29 6.191151E−34 −1.998284E−38 M6−1.683381E−25   8.658821E−31 −3.676860E−36  −5.905802E−41

The projection optical system 7 shown in FIG. 6 is a six-mirror system,like that shown in FIG. 5. In this case, the first mirror group 24 alsoincludes only the mirrors M1 and M2. The two mirrors M1 and M2 aresupplied off-axis.

The mirror M1 is arranged adjacent to the opening 21 of the mirror M4.This arrangement is such that the opening 21 of the mirror M4 is onlypassed through once for the ray between the mirrors M2 and M3.

The projection optical system 7 shown in FIG. 6 has only a singleintermediate image plane 27, which is spatially arranged, like theintermediate image planes 23 in the embodiments shown in FIGS. 2 to 5,between the last mirror in the light path, i.e. the mirror M6, and theimage plane 9.

In the embodiment shown in FIG. 6, despite the fact that the opening 21of the mirror M4 is passed though by a light beam which has no focusthere and thus has a relatively large diameter, the fourth-last mirrorM3 is still the mirror which, with the outer edge 22 thereof, providesthe pupil obscuration of the projection optical system 7.

The projection optical system 7 shown in FIG. 6 has a numerical apertureof 0.55.

The distance between the fourth-last mirror M3 and the last mirror M6 isequal to approximately 22% of the distance of the object plane 5 fromthe image plane 9 in the embodiment of the projection optical system 7shown in FIG. 6. The distance of the intermediate image plane 23 fromthe image plane 9 is approximately 0.8 times the distance of the lastmirror M6 in the light path from the image plane 9.

The projection optical system 7 shown in FIG. 6 has a maximum (rms)wavefront error of 1.4 nm. The maximum distortion is 1.4 nm. The pupilobscuration is 16.8%.

FIG. 7 shows a further embodiment of a projection optical system 7.Components and features which correspond to those that have previouslybeen described with reference to FIGS. 1 to 5 have the same referencenumerals and will not be discussed in detail again.

The optical data for the projection optical system 7 shown in FIG. 7 areshown in the following via two tables, which correspond in layout to thetables for FIG. 2.

Surface Radius (1/c) Thickness Operating mode Object plane infinity379.207 M1 −509.962 −179.207 REFL M2 −318.440 1332.984 REFL M3 343.817−1093.195 REFL M4 1475.059 2039.667 REFL M5 −609.119 −28.006 REFL stopinfinity −281.138 M6 562.495 354.144 REFL Image plane infinity 0.000

Surface K A B C M1  1.484533E−01 −5.739623E−10 9.023124E−14−7.365787E−18 M2  5.827688E−01  3.542976E−09 1.241138E−13 −3.596600E−17M3 −1.284995E+00 −4.653305E−09 1.019610E−13 −3.037140E−18 M4−4.865988E−02 −1.091347E−13 −6.628260E−21  −4.841711E−28 M5−4.572713E+00  2.517019E−09 7.268687E−16  6.794125E−19 M6  8.759896E−01 1.726609E−10 −2.501863E−15   1.688202E−20 Surface D E F G M13.807256E−22 −1.215662E−26 2.193281E−31 −1.712891E−36 M2 9.673512E−21−1.599535E−24 1.493641E−28 −5.987766E−33 M3 9.767861E−23 −2.436531E−273.766380E−32 −2.616614E−37 M4 −3.662658E−33  −1.445033E−38 1.208908E−44−4.273745E−51 M5 −1.846769E−23   4.603723E−28 −6.890055E−33  4.664473E−38 M6 1.453398E−25 −6.794812E−30 8.060319E−35 −3.545269E−40

Like the embodiments shown in FIGS. 5 and 6, the projection opticalsystem 7 shown in FIG. 7 is also a six-mirror system. The constructionof the first mirror group 24 comprising the mirrors M1 and M2corresponds to that of the embodiment shown in FIG. 6. The embodimentaccording to FIG. 7 also has only one intermediate image plane, namelythe intermediate image plane 27, which is arranged correspondingly tothat shown in FIG. 6.

The projection optical system 7 shown in FIG. 7 has a numerical apertureof 0.60.

The distance between the fourth-last mirror M3 and the last mirror M6 isequal to approximately 25% of the distance of the object plane 5 fromthe image plane 9 in the embodiment of the projection optical system 7shown in FIG. 7. The distance of the intermediate image plane 23 fromthe image plane 9 is approximately 0.8 times the distance of the lastmirror M6 in the light path from the image plane 9.

The maximum (rms) wavefront error of the projection optical system 7shown in FIG. 7 is 0.7 nm. The maximum distortion is 0.3 nm. The pupilobscuration is 16.0%.

To produce a microstructured or nanostructured component, the projectionexposure system 1 is used as follows: Initially, the reflection mask 10,or the reticle and the substrate, or the wafer 11 is prepared.Subsequently, a structure on the reticle 10 is projected onto alight-sensitive layer of the wafer 11 via the projection exposure system1. By developing the light-sensitive layer, a microstructure on thewafer 11, and thus the microstructured component, are then produced.

What is claimed is:
 1. An imaging optical system which during operationdirects light along a path to image an object field in an object planeto an image field in an image plane, the imaging optical systemcomprising: a plurality of mirrors positioned along an optical axis ofthe imaging optical system, where the plurality of mirrors direct thelight along the path, wherein at least three of the mirrors have anopening through which the light passes, each opening is completelysurrounded by a solid surface, and the imaging optical system forms atleast one intermediate image between the object plane and the imageplane, where the intermediate image that is closest to the image planein the light path is located between the image plane and the mirror thatis closest to the image plane along the light path.
 2. The imagingoptical system of claim 1, wherein the distance of the intermediateimage from the image plane is at most 0.95 times the distance, from theimage plane, of the last mirror in the light path.
 3. The imagingoptical system of claim 1, wherein: the plurality of mirrors comprisesat least six mirrors; and a fourth-last mirror along the path before theimage field does not include an opening and shadows a central portion ofa pupil plane of the imaging optical system.
 4. The imaging opticalsystem of claim 3, wherein the fourth-last mirror is a convex mirror. 5.The imaging optical system of claim 3, wherein the fourth-last mirror isarranged in the region of a pupil plane of the imaging optical system.6. The imaging optical system of claim 1, wherein the imaging opticalsystem has an image field-side numerical aperture of at least 0.4. 7.The imaging optical system of claim 1, wherein the imaging opticalsystem has a maximum root mean square wavefront error of less than 10nm.
 8. The imaging optical system of claim 1, wherein the imagingoptical system has a maximum distortion of less than 10 nm.
 9. Theimaging optical system of claim 1, wherein the imaging optical systemhas a pupil obscuration of less than 20%.
 10. The imaging optical systemof claim 1, wherein the image plane is parallel to the object plane. 11.The imaging optical system of claim 1, wherein the image field is largerthan 1 mm².
 12. The imaging optical system of claim 1, wherein the imagefield is a rectangular or arc-shaped image field with a side length of13 mm.
 13. The imaging optical system of claim 1, wherein the imagingoptical system has a reduction imaging scale of
 8. 14. The imagingoptical system of claim 1, wherein an odd number of mirrors of theimaging optical system have an opening through which the light passes.15. The imaging optical system of claim 1, wherein the at least oneintermediate image is in a plane that is folded in the vicinity of apupil plane of the imaging optical system.
 16. The imaging opticalsystem of claim 1, wherein principal rays in the light path between theobject plane and a first of the mirrors in the light path extenddivergently from neighbouring field points in the object field.
 17. Theimaging optical system of claim 1, wherein the imaging optical systemincludes exactly six mirrors and the imaging optical system images theobject field to exactly two intermediate image between the object planeand the image plane.
 18. The imaging optical system of claim 1, whereina third-last mirror and a fifth-last mirror along the path before theimage plane both include openings through which the light passes. 19.The imaging optical system of claim 1, wherein: the imaging opticalsystem comprises fewer than ten mirrors which direct the light along thepath; and the imaging optical system is a catoptric optical systemhaving an image field-side numerical aperture of ≧0.7.
 20. The imagingoptical system of claim 19, wherein the imaging optical system includesexactly eight mirrors and has an image field-side numerical aperture of0.9.
 21. A projection exposure system comprising: a light source; anillumination optical system; and the imaging optical system of claim 1,wherein during operation the light source provides light to theillumination optical system which directs the light to the object fieldof the imaging optical system, and the projection exposure system is aprojection exposure system for microlithography.
 22. The projectionexposure system of claim 21, wherein the light provided by the lightsource has a wavelength between nm 10 and 30 mm.
 23. A method forproducing a microstructured component, the method comprising: projectinga structure on a reticle onto a light-sensitive layer using a projectionexposure system, the projection exposure system comprising: a lightsource; an illumination optical system; and the imaging optical systemof claim
 1. 24. The imaging optical system of claim 1, wherein, for eachof the at least three mirrors, the mirror is configured so that, duringuse of the imaging optical system, the light is reflected by a portionof the solid surface that is adjacent to the opening.
 25. An imagingoptical system which during operation directs light along a path toimage an object field in an object plane to an image field in an imageplane, the imaging optical system comprising: a plurality of mirrorspositioned along an optical axis of the imaging optical system, wherethe plurality of mirrors direct the light along the path, wherein atleast three of the mirrors have an opening through which the lightpasses, the imaging optical system forms at least one intermediate imagebetween the object plane and the image plane, where the intermediateimage that is closest to the image plane in the light path is locatedbetween the image plane and the mirror that is closest to the imageplane along the light path, and the imaging optical system has areduction imaging scale of
 8. 26. An imaging optical system which duringoperation directs light along a path to image an object field in anobject plane to an image field in an image plane, the imaging opticalsystem comprising: a plurality of mirrors positioned along an opticalaxis of the imaging optical system, where the plurality of mirrorsdirect the light along the path, wherein: at least three of the mirrorshave an opening through which the light passes; the imaging opticalsystem forms at least one intermediate image between the object planeand the image plane, where the intermediate image that is closest to theimage plane in the light path is located between the image plane and themirror that is closest to the image plane along the light path; and theimaging optical system includes exactly six mirrors and the imagingoptical system images the object field to exactly two intermediate imagebetween the object plane and the image plane.
 27. An imaging opticalsystem which during operation directs light along a path to image anobject field in an object plane to an image field in an image plane, theimaging optical system comprising: a plurality of mirrors positionedalong an optical axis of the imaging optical system, where the pluralityof mirrors direct the light along the path, wherein: at least three ofthe mirrors have an opening through which the light passes; the imagingoptical system forms at least one intermediate image between the objectplane and the image plane, where the intermediate image that is closestto the image plane in the light path is located between the image planeand the mirror that is closest to the image plane along the light path;the imaging optical system comprises fewer than ten mirrors which directthe light along the path; and the imaging optical system is a catoptricoptical system having an image field-side numerical aperture of ≧0.7.28. The imaging optical system of claim 27, wherein the imaging opticalsystem includes exactly eight mirrors and has an image field-sidenumerical aperture of 0.9.